We have purified and characterized an extracellular selenium dependent glutathione peroxidase (EGPX) which is found in plasma, breast milk and lung luvage fluid. The plasma EGPx is made in the proximal convoluted tubule cells of the kidney, and EGPx has also be found to be secreted by lung epithelial cells. We have also demonstrated that EGPx is secreted through the basal-lateral membranes of proximal tubule cells. The overall goal of this proposal is to determine how this enzyme is secreted into extracellular fluid, and to examine the relationship of the synthesis and secretion of EGPX to changes in renal function, especially proximal tubular function. We will determine the structural elements of EGPx that directs its secretion through the basal-lateral membrane by constructing and transfecting chimeric proteins in proximal and distal tubule cells in culture. We will also inactivate the EGPx gene in mice by gene targeting. The consequences of EGPX inactivation on renal proximal tubular function, and renal and pulmonary development will be examined. Both control and EGPX deficient mice will be exposed to physiologic stressors, oxidizing agents and to agents known to cause proximal tubular damage. Renal function and renal and plasma lipid and protein peroxidation will then be determined. To test the hypothesis that the effect of nephrotoxic agents is on the synthesis or secretion of EGPX, the effects of experimental renal tubular damaging agents on the in vitro model of EGPx secretion will also be monitored. kility of EGPX activity as an index of drug-induced and other forms of proximal tubular injury.